Polyester/polyamide composite fiber has a problem of separation, also called fibrillation or pre-splitting, between the polyester component and the polyamide component. According to U.S. Pat. No. 3,489,641 to Harcolinski et al, this problem is due to inherent incompatibility, and may be overcome by use of a certain modified polyester. Harcolinski et al describe nylon 6.6, nylon 6, and polyhexamethylene-suberamide as especially suitable polyamides for combination with the modified polyester.
Southern, Martin and Baird, Textile Research Journal, pp. 411 (1980) describe improved sheath/core adhesion by the use of interface mixing after forming a composite melt stream. Nylon 6.6 sheath/PET core heterofil is spun. However, this approach is commercially difficult when spinning multiple monofils from a single spinneret.
U.S. Pat. No. 4,610,925 to Bond teaches that a nylon sheath on a polyester core will lack the required sheath/core adhesion. Bond describes avoiding the adhesion problem by using either a nylon core with a sheath made from nylon 11, nylon 12, nylon 6.10 or nylon 6.12, or a polyester core with a sheath made from copolyetherester. Bond provides the sheath/core filament thereof with antistatic characteristics by the addition of 20 to 30 wt. % carbon to the sheath.
U.S. Pat. No. 4,457,974 to Summers teaches the use of polyester substantially free of antimony to overcome pre-splitting, and describes nylon 6.6, nylon 6, and poly(hexamethylene sobacamide) as suitable polyamides for the polyester/polyamide composite fiber. In the Background portion of the patent, summers observes that pre-splitting can be reduced by including aminopropylmorpholine and bis-hexamethylenetriamine in the nylon component.
According to U.S. Pat. No. 5,380,477 to Kent et al, bicomponent spinning will allow two normally incompatible polymers to form strong materials without the use of compatibilizing agents. Kent et al broadly describe a matrix component selected from virtually any thermoplastic material, for instance, polyamides (such as nylon 6, nylon 6.6, nylon 6.6T, nylon 4.6, nylon 8, nylon 6.10, nylon 11 and nylon 12), polyolefins (such as polypropylene, polyethylene, polytetrafluoroethylene and polyphenylene ether), polyesters, polyimides, polysulfones, polyphenylenesulphide, polyvinyls, polyethyleneglycol, styrene-containing copolymers and so forth, and copolymers and blends. The examples teach a bicomponent fiber consisting of a PET core and a nylon 6 sheath, but sheath/core separation during stretching or drawing of this fiber, and in use, is overlooked.
Despite advances in the prior art, there continues to be a need for commercially advantageous, polyester/polyamide composite fiber, and in particular for core/sheath heterofil. While there are polyamides that adhere to polyesters, they are expensive specialty polymers, some also of poor physical properties; thus, a need exists for producing adhesion between polyesters and inexpensive commodity polyamides such as nylon 6 and nylon 6.6, with good physical properties.